User licensing offerings
A Client Access License (CAL) is required for each user or device accessing the Lync Server. There are three CAL offered with Lync Server 2010:
Lync Server 2010 Standard CAL: The Lync Server 2010 Standard CAL offers instant messaging and rich presence (IM/P) features. It provides users with real-time presence and enhanced IM along with PC-to-PC audio and video communications, as well as authenticated attendee experience for internally hosted conferences.
Lync Server 2010 Enterprise CAL: The Lync Server 2010 Enterprise CAL offers Audio, Video, and Web conferencing features. It provides users the ability to create, moderate, and join conferences for collaboration with both internal and external users.
Lync Server 2010 Plus CAL: The Lync Server 2010 Plus CAL offers enterprise voice telephony features. It provides high-quality voice and other related features to users anywhere with an Internet connection across IP phones, PCs, and desktop applications.
Lync Server 2010 offerings
Standard Edition
A Standard Edition server is ideal for pilot and lab deployments or branch offices that do not have high availability and performance requirements. It is intended for deployments with fewer than 5,000 users either in total or at a particular location.
Enterprise Edition
An Enterprise Edition server has all of the Standard Edition server features, and also provides scalability and high availability. It is intended to allow an unlimited number of users in any location or configuration.